The present invention relates to carriers used in the two-component developing method, in particular carriers coated with polyolefinic resins.
A two-component developing method, in which insulating nonmagnetic toners are mixed with carrier particles to frictionally charge the toners and the developers are carried and brought into contact with a electrostatic latent image to develop the electrostatic latent image, has been known as an electrostatic latent image-developing method.
Particulate carriers used in such the two-component developing method have been usually coated with suitable materials on account of reasons such as the prevention of toners from filming on a surface of carriers, the formation of a surface in which carriers are uniformly distributed, the prevention of a surface oxidation, the prevention of a reduced resistance to humidity, the prolongation of a useful life time of developers, the protection of a photoreceptor from a damage or an abrasion by carriers, the control of a chargeable polarity and the control of a charging quantity.
Polyolefinic resins have been known as such the coating materials (for example Japanese Patent Laid-Open No. Sho-52-154639, Japanese Patent Laid-Open No. Sho 54-35735 and the like).
Japanese Patent Laid-Open No. Sho 52-154639 discloses that polypropylene resins and the like are heated to be molten in suitable solvents and the resulting molten resins are spray-coated to carrier core materials to obtain carriers of which surface is coated with polypropylene resins.
Japanese Patent Laid-Open No. Sho 54-35735 discloses that coating material powders are stuck to a surface of carrier particles and heated at temperatures of a melting point of the coating material or more to be fixed, whereby obtaining coated carriers.
However, the carriers, of which surface is coated with polyolefinic resins in the above described manner, have shown disadvantages in that an adhesion of a coated layer to carriers is poor and a durability is inferior, for example, if the copying process is repeated, the coated material is separated. In addition, the above described methods have shown disadvantages in that for example the control of a film-thickness is not easy.